This bug reports corresponds to one opened on Gnome:

http://bugzilla.gnome.org/show_bug.cgi?id=578419

According to the devs there:

"As far as I can tell this is a Python/C bug.  PyGObject is doing
everything by
the book, and it is Python that is giving us corrupted base objects.  I
debugged long and hard but was unable to fix a bug that just isn't
there, nor
was I able to figure out a workaround."

I sure don't want this to get into a finger-pointing battle!  All I know
is that I can reproduce this at will. If the backtrace is not enough to
narrow down the cause of failure, please let me know what you would
need.  I'll be glad to help solve the problem.